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Mrs. and Mr. Stein -2- October 28, 1983 <br />in the fall of 1981, we were of the opinion that all the concerns <br />had been adequately addressed. As I believe you are aware, <br />Grand Mesa and the county participated equally in the road paving <br />project and, based on your August 18th letter, we believe that you <br />are satisfied with this. Grand Mesa was not aware of your additional <br />concern about fan noise until you called Mr. Reschke in August of <br />this year. We have looked at the options for further noise reduction, <br />and have specifically looked at the possibility of shutting dovm the <br />mine fan on idle shifts as long as potential coal sales for the mine <br />are limited. After carefully looking at this, Grand Mesa is of the <br />opinion that stopping mine ventilation on a daily basis would cause <br />adverse effect on mine roof conditions, due to the humidity change <br />that would be caused in the mine by starting and stopping the mine <br />fan. Specifically, the effect relates to roof rock deterioration <br />with resulting roof falls, which create obvious safety concerns and <br />significant additional costs for maintenance. We think that shutting <br />down of the fan is not a reasonable approach for us to take. <br />In light of that, we are looking at a two-phase program of addi- <br />tional noise reduction. As you know from the 1981 meetings, the mine <br />fan was equipped with a conical silencer that works much like a <br />silencer on a hand gun. It is a structure consisting of a sandwich <br />of materials including an exterior steel liner, a layer of noise <br />attenuation material, and an expanded metal interior lining. Also, <br />the acoustical block wall barrier was constructed at the discharge end <br />of the mine fan to dampen and re-direct the fan noise. The design of <br />the wall was modified after the June 23, 1981 meeting to direct the <br />noise in a southeasterly direction (away from as many residences as <br />possible). You mention in your letter that that barrier is of little <br />or no value. The wall does reduce the noise level several decibels, <br />and we are satisfied that it is an effective part of our overall noise <br />reduction plan. This data is also available at the mine office if you <br />wish to review it. <br />What we have decided to do, then, in Phase I is to build a block <br />house around the mine fan motor and belt drive system. That structure <br />will be treated with acoustical material, which will muffle noise <br />generated from the motor and the belt drive. We plan on doing this <br />construction and noise reduction project prior to the end of 1983. In <br />the first quarter of 1984 we will re-assess noise levels in the general <br />region. If those levels, after the Phase I reduction program, are found <br />not to be acceptable, we plan to construct an addition to the existing <br />acoustical wall in the second quarter, 1984. Both existing and new <br />portions of the wall will be insulated with sound attenuation material. <br />We would be happy to meet with you further, have you review the <br />plans or data in more detail, or pursue any other thoughts that you <br />have. <br />Sincerely, <br />J. F. Reynolds <br />cc: L. Reschke, Mine Engineer, WACC/ D. Groh, E.P.A./ D.Gourdin, <br />Colorado Health Department/ D. Mathe~ h1LRD <br />